Add customer login activity logging

- Add CustomerLoginLog model to track customer login attempts
- Record successful and failed customer logins
- Capture email, IP address, and user agent for each attempt
- Create /admin/customer-login-logs page to view activity
- Show login stats (successes, failures, active customers)
- Display browser/device and IP for each login attempt
- Add "Customer login activity" link to admin menu
- Monitor customer access patterns and detect suspicious activity
- Last 30 days active customer count

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

prisma/schema.prisma

@@ -393,3 +393,14 @@ model AdminLoginLog {
   userAgent String?
   success   Boolean  @default(true) // false for failed login attempts
 }
+
+// Audit log for customer logins — tracks customer account access
+model CustomerLoginLog {
+  id        String   @id @default(cuid())
+  customerId String?
+  email     String   // captured for failed attempts where customer doesn't exist
+  loginAt   DateTime @default(now())
+  ipAddress String?
+  userAgent String?
+  success   Boolean  @default(true) // false for failed login attempts
+}